1. Field of the Invention
On scale model airplanes which are used in wind tunnel testing to simulate or predict certain aerodynamic characteristics of the full-sized airplane, there is considerable difficulty in accurately producing a transition point on the model surface; and this invention relates to an improved method for applying turbulators to the model airfoil surfaces. Turbulators are used on the scale model airplane to simulate the transition point that occurs on the full-sized airplane, and this transition point is where the boundary layer airflow adjacent to the surface goes from a laminar airflow condition to a turbulent airflow condition, and this occurs at a percentage of the airfoil chord.
2. Description of Prior Art
One known method for producing a transition point of laminar airflow to turbulent airflow on a wing surface of a wind tunnel test model is to bond a narrow strip of sandpaper spanwise along the surface of the wing being tested.
Another known method is to apply an adhesive band spanwise along the surface of the model wing and then sprinkle grit onto the adhesive to produce a rough textured strip for producing some type of airflow agitation, hopefully resulting in a transition point. However, one problem with the sprinkled grit method is that the resulting rough textured strip varies depending upon the person applying it.
Both the sandpaper method and the sprinkled grit method either wear away rapidly or particles thereof are knocked off by the debris in the high velocity airflow of the wind tunnel; also, due to the duration of the wind tunnel tests, the grit particles wear away and have to be replaced to the original grit texture, which is generally not possible because of the human inconsistency element.
In order to eliminate the problems associated with the aforesaid sandpaper and sprinkled grit methods, another known method was developed wherein small diameter disks of aluminum were individually bonded onto the model surface. This method was a great improvement and produced predictable and repeatable results; and, in addition, the aluminum disks were much more durable from the standpoint of wear and being knocked off by debris. However, there is still a large factor of diversity associated with this aluminum disk method due to: the amount of adhesive applied to each individual aluminum disk; the size of the fillet of adhesive around the base of the disk; and the variations in spacing distances between the disks caused by their individual positioning by hand.
The present invention is a further inprovement over the aluminum disk method by solving the diversity problem through the use of a perforated tape mask and the in situ forming of the disks. Further, the need for the separate application of an adhesive to the disks for bonding to the model surface is eliminated by using an epoxy or an epoxy plus metal powder mixture squeegeed into the disk-sized perforations in the tape mask. The overall time of the in situ forming of the epoxy disks is drastically decreased from the aforesaid methods for producinq a transition point on a model surface; and the reproduction consistency of the epoxy disk method is substantially less dependent upon the worker's expertise.